Symbion pandora is a species of animal that lives on the whiskers of a lobster, feeding off the crumbs of its meals. Discovered in 1995, Symbion is so different from other species that it was assigned its own phylum, Cycliophora. It is only a half a millimeter long, but has reproductive habits that belong in science fiction. An adult can produce any of three types of offspring: pandora larva, prometheus larva, or female.

The Pandora larva develops into another feeding adult – a straightforward case of asexual reproduction. By contrast, the female remains inside the adult and awaits a male – but, attentive readers will be crying, what male?

The answer lies in the Prometheus larva. This attaches itself to another feeding adult, then produces two or three males from within itself. These dwarf males, which are even more internally complex than the other stages, seek out the females and fertilise them – though the details are unknown.

Once the female has been fertilised, she leaves the adult's body and hunkers down in a sheltered region of the lobster's mouthparts. Her body, no longer needed, turns into a hard cyst. Inside this, a fertilised egg develops into yet another stage: the chordoid larva.

In due course this larva hatches and swims off to colonise another lobster. Once it has attached itself to one, it develops into another adult and the cycle begins again.

@ hobbes3:Many parasites have crazy reproductive cycles like this. I recently read "Parasite Rex" by Carl Zimmer where he describes many strange parasitic species and their big and often underestimated influence on many ecosystems - quite an interesting book!